Pros: Great, clear and transparent sound, drives speakers and a wide range of headphones, you get to build your own, you can customise its appearance
Cons: May be a little lean on the bass for some, especially compared to the Bottlehead Crack
The Bottlehead S.E.X. is the mid-level DIY tube headphone amp from Bottlehead USA. As per the very well-known Crack OTL amplifier, it's a kit that you build yourself, but it's a little more challenging than the Crack due to the extra components involved.
In short, the Crack and S.E.X. both have their own strengths, but the S.E.X. is a definite step up in overall sound (which is a major complement) and it drives all range of headphone impedances, unlike the Crack's limit to >300ohm units.
The S.E.X. offers accurate, transparent sound with great texture, staging and imaging while the Crack offers lusher mids and fuller bass.
I've created a full thread to discuss the Crack, the S.E.X., and soon the Mainline, Bottlehead's TOTL headphone amp.
You can view the full thread here: http://www.head-fi.org/t/683012/bottlehead-amplifier-discussion-comparison-thread-crack-sex-mainline
Or jump to the full S.E.X. review here: http://www.head-fi.org/t/683012/bottlehead-amplifier-discussion-comparison-thread-crack-sex-mainline#post_9831527